1. Technical Field
The present invention relates to a method of generating a time-division multiplexed encoded transmission signal that is used in a communication system where an optical time-division multiplexing method and an optical code-division multiplexing method are used together, and an apparatus for realizing the same.
2. Related Art
In recent years, with the development of the Internet, communication demands have rapidly increased. For this reason, a communication capacity has increased. As an example of a method for increasing the communication capacity, optical multiplexing technologies for collectively transmitting optical pulse signals corresponding to plural channels through one optical fiber transmission path have attracted attention.
As the optical multiplexing technologies, an optical time-division multiplexing (OFDM) scheme, a wavelength-division multiplexing (WDM) scheme, and an optical code division multiplexing (OCDM) scheme have been actively studied.
According to the optical multiplexing technologies, optical pulse signals corresponding to plural channels may be collectively transmitted through one optical fiber transmission path. Accordingly, the communication capacity may be increased while the existing communication network is maintained as it is. If these optical multiplexing technologies are combined, the communication capacity may be further increased.
Accordingly, a communication system where the OTDM scheme and the OCDM scheme are used together is suggested (for example, refer to “Study Of OTDM Channel Identifying Technique Using FBG Type Optical Encoder” in Ref. 1 Proceedings of the 2007 Communications Society Conference of the Institute of Electronics, Information and Communication Engineers, B-10-60).
In the communication system where the OTDM scheme and the OCDM scheme are used together, in order to efficiently realize the OTDM scheme, the time delay amount of an encoded transmission signal of each channel needs to be adjusted, such that the encoded signals of the individual channels are arranged at an equivalent interval on a time axis. In terms of effective utilization of communication resources, a time slot that is allocated to each channel may be minimized.
If the time slot that is allocated to each channel is minimally set, adjacent channels may overlap each other due to a change in a communication state. If the channels overlap, crosstalk may be generated between the adjacent channels. If the time slot is secured to be excessively wide, the time slot includes an unnecessary time zone, although the adjacent channels do not overlap each other. Accordingly, this becomes an obstacle when communication resources are effectively used and communication efficiency is improved.
In order to minimize the time slot and prevent the crosstalk from being generated between the adjacent channels, such that the encoded transmission signals of the individual channels may be dynamically adjusted so that they are arranged at an equivalent interval on the time axis. The optimal positions of the encoded transmission signals of the individual channels on the time axis are momentarily changed according to a communication state.
Accordingly, in the communication system where the OTDM scheme and the OCDM scheme are used together, the time delay added to the encoded transmission signals of the individual channels need to be flexibly changed according to the momentarily changed communication state, such that the encoded transmission signals of the individual channels are arranged at the equivalent interval on the time axis.
However, in the communication system where the OTDM scheme and the OCDM scheme are used together, a method that adjusts the encoded transmission signals of the individual channels to be arranged at the equivalent interval on the time axis has not been proposed.